Modulation Study On Unsubmerged Cavitating Jet From Nozzle With A Centre Cylinder

Cavitation water jets from nozzle with a centre cylinder is a type of cavitation jets.Based on abundant investigations of water jets from nozzle with a centre cylinder, the influence law of hydraulic and structural parameters on effect of rock breaking under water jet is researched through some numerical simulations and experiments. And structural parameters of nozzle with a centre cylinder are optimized by simulations and experimental results. Numerical simulations adopt k -εstandard model and mixture multiphase flow governing equations. The results indicate that non-submerged conditions heighten effective standoff distance of water jet from nozzle with a centre cylinder. The pressure field and velocity field shows the complexity of change.At beginning, axis lines of water jet appear negative pressure region, then pressure along the axial increases till to maximum positive pressure, subsequently, it drops rapidly to environmental pressure.In small range of standoff distance, velocity of flow in axis lines of nozzle jet first increases then decreases rapidly, when it reduces to a minimum value, velocity rapid increases rapidly, at around 4～5 dimensionless Dn maximum.By non-submerged water jet pressure rock breaking experiment through a nozzle with a centre cylinder, we find that when optimal standoff distance is between 1 dimensionless Dn and 2 dimensionless Dn, the effect of rock breaking is better than conventional non-submerged jet, which showing that nozzle with a centre cylinder has potential of producing cavities.In case of the same operating parameters, the rock breaking ability of nozzle with a centre cylinder relates to outlet length and diameter of nozzle, diameter and embedded depth of centre cylinder, etc. Experiment shows that when nozzle outlet length L is between 1 and 1.5 equivalent Dn, diameter ratio of centre cylinder to nozzle Dc/Dn is between 0.5 and 0.75 and embedded depth of centre cylinder is between 0.4Dn and 0.7Dn, the rock breaking effect of nozzle is better. The results of numerical simulation agree well with rock erosion experiments. Providing a new direction for improving the effect of jet breakability under non-submerged condition.